diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -3500,6 +3500,13 @@
 
 // Microsoft-related attributes
 
+def MSConstexpr : InheritableAttr {
+  let LangOpts = [MicrosoftExt];
+  let Spellings = [CXX11<"msvc", "constexpr">];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [MSConstexprDocs];
+}
+
 def MSNoVTable : InheritableAttr, TargetSpecificAttr<TargetMicrosoftCXXABI> {
   let Spellings = [Declspec<"novtable">];
   let Subjects = SubjectList<[CXXRecord]>;
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -3478,6 +3478,14 @@
 }];
 }
 
+def MSConstexprDocs : Documentation {
+  let Category = DocCatStmt;
+  let Content = [{
+This attribute is an alias of ``constexpr`` for functions.
+Available only as Microsoft extension (``-fms-extensions``).
+  }];
+}
+
 def MSNoVTableDocs : Documentation {
   let Category = DocCatDecl;
   let Content = [{
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -4992,6 +4992,9 @@
   case ParsedAttr::AT_PreserveAll:
     D->addAttr(::new (S.Context) PreserveAllAttr(S.Context, AL));
     return;
+  case ParsedAttr::AT_MSConstexpr:
+    D->addAttr(::new (S.Context) MSConstexprAttr(S.Context, AL));
+    return;
   default:
     llvm_unreachable("unexpected attribute kind");
   }
@@ -7050,6 +7053,12 @@
   D->addAttr(::new (S.Context) ThreadAttr(S.Context, AL));
 }
 
+static void handleMSConstexprAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+  if (auto *FD = dyn_cast<FunctionDecl>(D))
+    FD->setConstexprKind(ConstexprSpecKind::Constexpr);
+  D->addAttr(::new (S.Context) MSConstexprAttr(S.Context, AL));
+}
+
 static void handleAbiTagAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   SmallVector<StringRef, 4> Tags;
   for (unsigned I = 0, E = AL.getNumArgs(); I != E; ++I) {
@@ -8987,6 +8996,9 @@
   case ParsedAttr::AT_Thread:
     handleDeclspecThreadAttr(S, D, AL);
     break;
+  case ParsedAttr::AT_MSConstexpr:
+    handleMSConstexprAttr(S, D, AL);
+    break;
 
   // HLSL attributes:
   case ParsedAttr::AT_HLSLNumThreads:
diff --git a/clang/test/AST/msvc-attrs.cpp b/clang/test/AST/msvc-attrs.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/AST/msvc-attrs.cpp
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -fms-extensions -std=c++20 -ast-dump %s | FileCheck %s
+// RUN: not %clang_cc1 -Werror=ignored-attributes -ast-dump %s 2> %t.stderr.txt
+// RUN: FileCheck -check-prefix CHECK-DIAG-NO-MSX %s < %t.stderr.txt
+
+// CHECK: msvc-attrs.cpp:[[@LINE+3]]:21, col:61> col:27 constexpr New1 'void *(void *)'
+// CHECK: MSConstexprAttr 0x{{[0-9a-f]+}} <col:3, col:9>
+// CHECK-DIAG-NO-MSX: msvc-attrs.cpp:[[@LINE+1]]:3: error: 'constexpr' attribute ignored
+[[msvc::constexpr]] void *New1(void *where) { return where; }
diff --git a/clang/test/Misc/pragma-attribute-supported-attributes-list.test b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
--- a/clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -83,6 +83,7 @@
 // CHECK-NEXT: LoaderUninitialized (SubjectMatchRule_variable_is_global)
 // CHECK-NEXT: Lockable (SubjectMatchRule_record)
 // CHECK-NEXT: MIGServerRoutine (SubjectMatchRule_function, SubjectMatchRule_objc_method, SubjectMatchRule_block)
+// CHECK-NEXT: MSConstexpr (SubjectMatchRule_function)
 // CHECK-NEXT: MSStruct (SubjectMatchRule_record)
 // CHECK-NEXT: MaybeUndef (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: MicroMips (SubjectMatchRule_function)